The present invention relates to improvements in a printing apparatus for printing a running web.
FIG. 1 shows a conventional color printing apparatus in which as the web 4 to be printed passes between an impression cylinder 1 and plate cylinders 2, it is printed by plates 3 mounted on the plate cylinders. The impression cylinder and the plate cylinders are driven from a single motor through a geared transmission for synchronized printing. Since the circumference of the plate cylinders is determined by the printing length which is the length of the plate, each time the printing length changes, new plate cylinders having a circumference corresponding to the new printing length become necessary. This increases the printing cost. Further, each time the printing length changes, heavy plate cylinders have to be removed and replaced with new ones. New plate cylinders with new plates mounted thereon have to be mounted on the impression cylinder with a suitable contact pressure. This was very troublesome work. Further, fine adjustments of the transmission were necessary for phase tuning between the plate cylinders for accurate register. Another disadvantage is that a lot of plate cylinders have to be maintained.